def prost(x):
    k = 0
    for d in range(1,x+1):
        if x % d == 0:
            k+=1
    if k == 2:
            return True
    else:
            return False
        
first_num = 0
second_num = 0
num = ''
s = input().split()
sp_chis = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']
if len(s)!= 3 or s[0]== '0':
    print('wrong_input')
else:
    for i in s:
        if i in sp_chis:
            num+=str(sp_chis.index(i))
    for p in range (int(num)+1, 1000):
        if prost(p)==True:
            first_num = p
            break
    if abs(int(num) - first_num) >= abs(int(num) - second_num):
        print(second_num)
    else:
        print(first_num)
